I bought a plug in hybrid towards the end of last year. Since Easter it has occasionally failed to fully charge overnight. I was thinking that it might need to be checked out and then last night I suddenly realised what was going wrong. Sometimes I pick DD up from school and she leaves her bag in the car, so she has to go out later in the evening and get it. But, of course, when she unlocks the car it stops charging and quite often it wouldn't have completed its charge by that stage.
I'm glad I realised that now rather than bringing it in to the garage when there's nothing actually wrong with it. 